High-voltage insulator terminal



S. WALD HIGH VOLTAGE INSULATOR TERMINAL Filed Feb. 27, 1946 Jan. 31, 1950 IN VEN TOR. gfikzney Wald II'IOE/YEV Patented Jan. 31, 1950 HIGH-VOLTAGE INSULATOR TERMINAL Sidney Wald, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application February 27, 1946, Serial No. 650,709

This invention relates to improvements in high voltage insulator terminals. More particularly, it relates to insulator terminals designed to terminate the high voltage output of aircraft transmitters.

The use of high voltage electrical equipment always brings accompanying problems of providing proper insulation which will not break down under the severe conditions imposed. Ordinary insulators which provide for a high safety factor at 115 v. may be entirely useless at voltages in the thousands. However, in the case of high voltage equipment to be used in aircraft which may ascend to altitudes of 40,000 feet, the insulation problems are multiplied. This is due to the surrounding air being rarefied and hence subject to ionization at much lower voltages than is the case with air at sea level. For example, at an altitude of 40,000 feet, the voltage of corona formation around a conductor is only about 0.3 the corona voltage at sea level.

For this reason, particular care must be taken in designing high voltage equipment to be used in aircraft. All metal conductors must have sufflcient safety factors which will preclude possibility of arc-over at the maximum altitude at which the plane is able to fly.

One place that such provision must be made is in the instance of terminals which are to be used in leading out high voltage currents from the aircrafts transmitter to its antenna. One conventional solution to a problem of this type is to use large radius conductors such as copper or brass tubing and also to provide wide spacing between metal parts and between conductors and grounded parts. This type of equipment is commonly used for supplying and controlling high voltages used in electron microscopes, for example. But these expedients are not suitable for use in aircraft transmitters since such equipment must be designed to have minimum weight and occupy as little space as possible.

Accordingly, it is an object of the present invention to provide a high voltage insulator terminal which is light and compact.

It is another object to provide a high voltage insulator terminal especially adapted to be used on aircraft transmitters.

It is a further object to provide a high voltage terminal which fully protects the user against the efiects of accidental contact.

It is still another object to provide a high voltage terminal which is so formed and sealed as to retain normal or above normal atmospheric prespost 3.

t 5 Claims. (01. 174-31) sure inside even when exposed to rarefied air on the external surface.

Other objects and advantages will become more apparent and the invention will be better understood from the following description and the accompanying drawings of which Fig. 1 is a cross section view of a preferred form of insulator constructed according to the inven- [tion and shown attached to a transmitter cabinet.

Fig. 2 is a perspective view showing how the insulator terminal may be used to connect the external antenna lead on a high voltage generator to be used in aircraft.

As shown in Fig. 1', hollow ceramic base i has within it a conductor 2 terminating in binding A curved metal shield 4 surrounds the end of the conductor and the binding post. In one end of the metal shield is an opening 5 through which a connecting conductor may be inserted to be attached to binding post 3.

' Attached to the end of the metal shield op'po site from opening 5 is a thin insulating cap 6 which is attached inside the shield by a projection which extends through opening I and which it attached to a metal holding block 8 by means of a threaded shaft 9.

The particular form of insulator illustrated is intended to be used on the outside of a high voltage transmitter as the lead-in terminal for the antenna, although obviously it is not restricted to this specific use. As shown in Figs. 1 and 2, it is attached to the outside of the transmitter cabinet I0 and has attached to it one end of antenna lead l2. Transmitter cabinets containing high voltage generating apparatus designed for use in aircraft usually are hermetically sealed and the interior is put under a pressure slightly higher than ordinary atmospheric pressure at sea level. Then, no matter how high the aircraft may fly, the tendency for the insulation inside the cabinet to break down is not increased since the surrounding air pressure remains constant and at a desirably high level.

As also shown in the cross section view of Fig. 1, the hollow ceramic base of the insulator terminal communicates by means of opening II in the transmitter cabinet with the cabinet interior and the air pressure within the base of the terminal is therefore the same as that inside the cabinet.

This provision for maintaining above-normal air pressure within the base of the insulator terminal obviates the danger of arc-over at the high voltages used even though the conductor is a slender wire and the ceramic walls are thin and light. The use of the smoothly curved metal shield with its minimum voltage gradient enables an ordinary binding post to be used for attaching the lead-in conductor to the high voltage output and no attention need be given to the sharp edges and corners which such conventional binding posts contain. The insulating shield which may be of polyethylene, polystryrene or some other plastic having low dielectric constant protects the one who must use the equipment from the dangers of shock should he accidentally touch the terminal. The insulating shield, since it is constructed of a material having a low dielectric constant, may be made very thin. Therefore, it does not alter smoothly rounded contour of the metal shield to any appreciable extent.

The insulator terminal, which has been described, may be used with any high voltage equipment but is of particular value inconnection with pressurized cabinets because of its provision for pressurizing the base of the terminal. It operates well in equipment flown at altitudes as great as 50,000 feet and using 7,000 or more volts output. The cabinet and the interior are preferably always under an internal pressure higher than the surrounding air. This condition is usually present in pressurized transmitter cabinets since the pressure within is usually a little greater than normal atmospheric pressure at sea level.

One advantage in the design of the insulator terminal disclosed is its relatively small size compared with the voltages it is designed to handle. For use with 7,000 volts output the overall height of the terminal may be no more than 2 inches while the diameter of the ceramic base may be only 1.5 inches.

There has thus been described a high voltage insulator terminal which is so small and compact that it may be used on aircraft transmitters but which is perfectly safe at all operating 4 voltages and which will not fail at high altitudes.

I claim as my invention:

1. A high voltage insulator terminal comprising an insulating base member surrounding an electrical conductor, a binding post surmounting said base member and connected to said conductor, a smoothly curved metal shield enclosing said binding post, an insulating cap at least partially covering said shield and means entirely within said shield for securing said cap against said shield.

2. A high voltage terminal comprising a high voltage conductor, a binding post terminating said conductor, a smoothly curved metal shield surrounding said binding post said shield having an opening therein, an insulating cap external to and concentric with said shield said cap including projection adapted to extend through said opening and means entirely within said shield for securing said cap against said shield.

3. A terminal according to claim 2 in which said cap only partially covers shield.

4. A terminal according to claim 2 in which said cap is relatively thin and is composed of a material having a relatively low dielectric constant.

5. A terminal according to claim 4 in which said material is polystyrene.

SIDNEY WALD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,522,215 Wagner Jan. 6, 1925 FOREIGN PATENTS Number Country Date 70,492 Sweden Oct. 28, 1930 314,893 Great Britain Feb. 28, 1930 

